Unlike conventional random access memory (RAM) chip technologies, in magnetic RAM (MRAM) data is stored by magnetic polarization of storage elements. The storage elements are formed from two ferromagnetic layers separated by a tunneling layer. One of the two ferromagnetic layers, which is referred to as the fixed (e.g., pinned) layer, has a magnetization that is fixed in a particular direction. The other ferromagnetic magnetic layer, which is referred to as the free layer, has a magnetization direction that can be altered to two different states. One such device having a fixed layer, a tunneling layer, and a free layer is a magnetic tunnel junction (MTJ).
In an MTJ, the different states of the free layer may be used to represent either a logic “1” or a logic “0”. In particular, the electrical resistance of an MTJ depends on whether the free layer magnetization and fixed layer magnetization are parallel or anti-parallel with each other. For example, a logic “1” state is represented when the free layer magnetization is anti-parallel to the fixed layer magnetization. A logic “0” state is represented when the free layer magnetization is parallel to the fixed layer magnetization. A memory device such as MRAM is built from an array of individually addressable MTJs.
To write data in a conventional MRAM, a write current exceeding a critical switching current is applied through an MTJ. The write current should exceed the switching current by a sufficient amount to change the magnetization direction of the free layer. When the write current flows in a first direction, the MTJ is placed into or remains in a first state. In the first state, a free layer magnetization direction and a fixed layer magnetization direction of the MTJ are aligned in a parallel orientation. When the write current flows in a second direction, opposite to the first direction, the MTJ is placed into or remains in a second state. In the second state, the free layer magnetization and fixed layer magnetization of the MTJ are in an anti-parallel orientation.